The present invention is directed to light reflectors and, in particular, to a split conic and/or aspheric reflector and method of performing post processing applications such as polishing and/or coating the reflecting surface.
Conic and/or aspheric reflectors, such as paraboloidal, ellipsoidal, and aspheric reflectors are commonly used in today""s data and video projection systems where efficient collection and redirection of light from a lamp is required. These reflectors are used in projection systems and spot (image projecting) luminaires. Such reflectors may also be used in other areas such as in entertainment lighting, such as, for example, wash luminaires, and in scientific illumination, such as, for example, high intensity light for spectroscopy. Current reflectors are made in large quantities by molding methods and in small quantities by electro-forming, pressing, diamond turning or other mechanical methods. In order to optimize the reflector""s efficiency, they are usually coated with multilayer optical coatings and are sometimes polished after molding but prior to coating.
FIG. 1 illustrates one type of device in which reflectors are used wherein an image projector 10 includes a high power lamp 12 that employs a one-piece reflector 14. The lamp 12 produces a high powered beam 16 that propagates through a rotating color wheel 18 of a color wheel assembly 20. Color wheel 18 includes at least three sectors, each tinted in a different one of three primary colors to provide a field sequential color image capability for image projector 10. The beam is directed by a mirror 32 that is inclined so that the beam propagates through a prism component 42 and through a projection lens 64 to a projector screen (not shown) to display an image to a viewer. Most reflectors 14 used in current image projectors 10 are molded as a one-piece unit. It is to be understood that the image projector 10 shown in FIG. 1 represents only one example of a device employing a reflector to which the invention is directed.
One problem that exists with reflectors that are molded in one piece is that it is difficult to remove the reflector from the mold. Typically, reflectors are molded by forcing molten glass into a metal mold having a cavity formed between an inner die core and an outer mold body. When the glass has cooled sufficiently the mold parts are pulled away from the reflector. It can be difficult to remove the reflector from the inner die core without breaking the reflector due to its shape. This problem is best illustrated in FIG. 2, which shows a molded glass reflector 80 and an inner die core 82. The glass reflector 80 is generally removed from the inner die core 82 by pulling it in the direction of arrow 84. A line of tangency 86 can be established at any point of contact between the inner surface 88 of the reflector 80 or the outer surface 90 of the inner die core 82 forming what is known as the draft angle 92 with a horizontal plane parallel to the direction of removal of the inner die core 82. As the draft angle 92 decreases, the friction between the reflector 80 and the inner die core 82 increases. There is a point at which the draft angle 92 cannot be less than a minimum without damage to the reflector 80. The minimum draft angle is determined by several factors such as, for example, the thickness of the glass and the length of the draft region. The minimum draft angle may vary a few degrees; however, it has been found that the preferred minimum draft angle is about 5 degrees. If the draft angle is less than about 5 degrees, the reflector 80 cannot be properly removed from the inner die core 82. This is difficult to achieve when fabricating one-piece reflectors because it would require the reflector 80 to have a less than desirable length resulting in less light collection and a less efficient projection system.
As shown in FIG. 2 the area represented at 96 illustrates draft region or the area of contact between the reflector 80 and the inner die core 82 in which the draft angle is about 4 degrees which is less than the preferred minimum draft angle, which may result in reflector breakage or loss.
Furthermore, the post processing operations such as polishing and coating of the reflectors becomes difficult as the diameter or overall size of the reflector decreases and as the depth or extent increases. The primary problem here is essentially one of not being able to adequately reach the entire interior reflecting surface.
It is therefore desirable to provide a conic and/or aspheric reflector that can be more readily removed from the mold. It is also desirable to provide such a reflector in which the reflective surface is more accessible for performing post processing operations such as polishing and coating.
The present invention provides for a method of manufacturing a conic and/or aspheric reflector in which the reflector is manufactured in two or more sections and later assembled to form a unitary reflector. Forming the reflector in sections eliminates the difficulty of removing the reflector sections from their associated mold caused by problems related to the draft angle.
Manufacturing the reflector in two or more sections also provides better access to the inner reflective surfaces of the sections for such post processing operations as polishing and coating the inner reflective surface.
Each section is accurately indexed with respect to the other section to achieve a smooth and continuous reflecting surface. The resulting assembled reflector accurately reproduces the shape of a one piece reflector.
The mating faces of the reflector sections can be ground, if necessary, after molding if they are not flat enough directly from the mold. It is important for the mating surfaces to be flat to achieve best optical efficiency. The gap between the mating faces of the reflector sections needs to be minimized in order to achieve a nearly continuous optical surface.
Additionally, light-blocking features can be added to the mating faces of the reflector sections to minimize and or eliminate any possible escape of light from the reflector. Such features may take a plurality of different geometrical forms. However, what is achieved by the light-blocking features is a surface in which there is no gap in the seam formed by the mating surfaces which allows light to escape. The light blocking features include some geometrical overlap along the mating edge seam to prevent stray light from escaping from the interior surface of the reflector through to the exterior of the reflector along the joint seam. Such light blocking configurations might include, for example, a lap joint, a V-groove joint, or curved mating surfaces.
The reflector sections may be held together and indexed relative to each other by various features such as, for example, pins that align with mating seats in an adjacent reflector section. Such alignment pins may be integral with the reflector section or may be separate and adhered or mechanically held in place. Other alignment features may include separate spheres, rivets, cones, truncated cones, wedges, and flats.
The present invention removes the limitation in the size and shape of conic and/or aspheric reflectors which can be cost effectively fabricated. The split conic and/or aspheric reflector approach allows small diameter and/or deep reflectors of this type to be more easily fabricated by either molding or direct machining and, if needed, more easily post-polished and coated. This is most beneficial when the length of extent of the reflector is large compared to the diameter of the reflector.
The split reflector assembly also may offer the benefit of reducing the level of thermal stress experienced by the assembled reflector compared to one piece reflectors. This is achieved by allowing the reflector to expand and/or contract due to heating or cooling without letting light escape from the reflector.
It is an object of this invention to provide a reflector for a projection system that is manufactured in at least two sections.
It is another object of this invention to provide a reflector that is manufactured by a method that provides ease of removal from a mold die.
Another object of this invention is to provide a reflector manufactured by a process that eliminates problems associated with the draft angle.
It is yet another object of this invention to provide a reflector for a projection system that is easily fabricated to provide access to the reflecting surface for post-fabrication processing such as polishing and coating.
Still another object of the invention to provide a split reflector for a projection system that has a substantially continuous reflecting surface.
It is a further object of the invention to provide a split reflector in which the mating surfaces include light blocking features to prevent light from escaping from the interior surface to the exterior of the reflector.
Yet another object of the invention is to reduce the level of thermal stress experienced by the assembled reflector.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.